Backus-Naur notation (shortly BNF) is a formal mathematical way to describe a language, (to The Backus-Naur Form is a way of defining syntax. It consists of. The standard technique for defining the syntax of a computer language is to use Backus-Naur Form (BNF). The variant used in this tutorial is as follows. A Practical Tutorial on Context Free Grammars. Robert B. . Backus-Naur Form ( BNF) is a notation for expressing a CFG. The notation.

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Backus-Naur Form (BNF)

Not to be confused with Boyce—Codd normal form. In the committee’s report, Peter Naur called Backus’s notation Backus normal form. It’s common to find regular-expression-like operations inside grammars. The ” ” symbol was originally the word ” or ” with a bar over it.

Naur changed two of Backus’s symbols to commonly available characters.

Grammar: The language of languages (BNF, EBNF, ABNF and more)

For the purpose of including text among the symbols of a program the following “comment” conventions hold:. This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November and incorporated under the “relicensing” terms of the GFDLversion 1. For an comprehensive treatment of parsing techniques, I recommend Grune and Jacobs, Parsing Techniques: The is used to separate alternative definitions and is interpreted as “or”.


Or even reordering an expression to group data types and evaluation results of mixed types. Even though some languages are context-sensitive, context-sensitive grammars are rarely used for describing computer languages. But, the reverse is not true: Meanwhile, string rewriting rules as formal, abstract systems were introduced and studied by mathematicians such as Axel Thue inEmil Post s—40s and Alan Turing In computer scienceBackus—Naur form or Backus tutkrial form BNF is a notation technique for context-free grammarsoften used to describe backue syntax of languages used in computing, such as computer programming languagesdocument formatsinstruction sets and communication protocols.

A class is an abstraction, we can talk about it independent of its formation. Retrieved from ” https: Anything other than the metasymbols:: By using this site, you agree to the Terms of Use and Privacy Policy. Chomsky terminology was not originally used in describing BNF. In EBNF, square brackets around an expansion, [ expansion ]indicates that this expansion is optional. These changes made that META II and flrm derivative programming languages able to define and extend their own metalanguage.

For more on this, see my article on translating math into code. English is only one of the possible natural languages. There are no specifics on white space in the above. Juxtaposition of marks or variables in a formula signifies juxtaposition of the sequence denoted. Retrieved May 11, Not all of these are strictly a superset, as some change the rule-definition relation:: Regular expressions sit just beneath context-free grammars in descriptive power: For describing ordinary natural languages designation like word, verb, noun, are used.


Archived from the original on 5 June Parsing expression grammars build on the BNF and regular expression notations to form an alternative class of formal grammarwhich is essentially analytic rather than generative in character. Many BNF specifications found bcakus today are intended to be human-readable and are non-formal. Formal languages Compiler construction Metalanguages.

The language of languages

BNF is a notation for Chomsky’s context-free grammars. Even when grammars are not an object of mathematical study themselves, in texts that deal with discrete mathematical structures, grammars appear to define new notations and new structures.

Symbols that never appear on a left side are terminals. Arithmetic like grouping provided simplification that removed using classes where grouping was its only value.